New antiviral pathway that mediates hepatitis C virus replicon interferon sensitivity through ADAR1.

CBER/FDA, HFM-448, 8800 Rockville Pike, Bethesda, MD 20892, USA.
Journal of Virology (Impact Factor: 4.65). 06/2005; 79(10):6291-8. DOI: 10.1128/JVI.79.10.6291-6298.2005
Source: PubMed

ABSTRACT While many clinical hepatitis C virus (HCV) infections are resistant to alpha interferon (IFN-alpha) therapy, subgenomic in vitro self-replicating HCV RNAs (HCV replicons) are characterized by marked IFN-alpha sensitivity. IFN-alpha treatment of replicon-containing cells results in a rapid loss of viral RNA via translation inhibition through double-stranded RNA-activated protein kinase (PKR) and also through a new pathway involving RNA editing by an adenosine deaminase that acts on double-stranded RNA (ADAR1). More than 200 genes are induced by IFN-alpha, and yet only a few are attributed with an antiviral role. We show that inhibition of both PKR and ADAR1 by the addition of adenovirus-associated RNA stimulates replicon expression and reduces the amount of inosine recovered from RNA in replicon cells. Small inhibitory RNA, specific for ADAR1, stimulated the replicon 40-fold, indicating that ADAR1 has a role in limiting replication of the viral RNA. This is the first report of ADAR's involvement in a potent antiviral pathway and its action to specifically eliminate HCV RNA through adenosine to inosine editing. These results may explain successful HCV replicon clearance by IFN-alpha in vitro and may provide a promising new therapeutic strategy for HCV as well as other viral infections.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Translation initiation of the Hepatitis C virus (HCV) genome is driven by an internal ribosome entry site (IRES), located within the 5' non-coding region. Several studies have suggested that different cellular non canonical proteins or viral proteins can regulate the HCV IRES activity. However, the role of the viral proteins on HCV translation remains controversial. In this report, we confirmed previous studies showing that NS5A down-regulates IRES activity in HepG2 but not in Huh7 cells suggesting that the NS5A effect on HCV IRES is cell-type dependent. Additionally, we provide strong evidence that activated PKR up-regulates the IRES activity while silencing of endogenous PKR had the opposite effect. Furthermore, we present data indicating that the NS5A-mediated inhibitory effect on IRES-dependent translation could be linked with the PKR inactivation. Finally, we show that NS5A from GBV-C but not from GBV-B down-regulates HCV IRES activity in the absence or the presence of PKR over expression. Notably, HCV and GBV-C but not GBV-B NS5A contains a previously identified PKR interacting protein domain.
    Infection, genetics and evolution: journal of molecular epidemiology and evolutionary genetics in infectious diseases 05/2014; · 3.22 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Type I interferon (IFN) production is one of the hallmarks of host innate immune responses upon virus infection. While most respiratory viruses carry IFN-antagonists, reports on human Metapneumovirus (HMPV) have been conflicting. Using deep sequencing we demonstrate that HMPV particles accumulate excessive amounts of defective interfering RNA (DIs) rapidly upon in-vitro passage, which are associated with IFN induction. Importantly, the DIs were edited extensively; up to 70% of the original A and T residues had mutated to G or C respectively. Such high editing rates of viral RNA have not been reported before. Bioinformatics and PCR assays indicated that Adenosine Deaminase acting on RNA (ADAR) is the most likely editing enzyme. HMPV thus has an unusually high propensity to generate DIs, which are edited at an unprecedented high frequency. The conflicting published data on HMPV IFN induction and antagonism are likely explained by DIs in virus stocks. The interaction of HMPV DIs with the RNA editing machinery and IFN responses warrants further investigation.
    Journal of General Virology 04/2014; · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background The role of innate immunity in general and of type I interferon (IFN-I) in particular in HTLV-1 pathogenesis is still a matter of debate. ADAR1-p150 is an Interferon Stimulated Gene (ISG) induced by IFN-I that can edit viral RNAs. We therefore investigated whether it could play the role of an anti-HTLV factor.ResultsWe demonstrate here that ADAR1 is also expressed in the absence of IFN stimulation in activated primary T-lymphocytes that are the natural target of this virus and in HTLV-1 or HTLV-2 chronically infected T-cells. ADAR1 expression is also increased in primary lymphocytes obtained from HTLV-1 infected individuals. We show that ADAR1 enhances HTLV-1 and HTLV-2 infection in T-lymphocytes and that this proviral effect is independent from its editing activity. ADAR1 expression suppresses IFN-¿ inhibitory effect on HTLV-1 and HTLV-2 and acts through the repression of PKR phosphorylation.DiscussionThis study demonstrates that two interferon stimulated genes, i.e. PKR and ADAR1 have opposite effects on HTLV replication in vivo. The balanced expression of those proteins could determine the fate of the viral cycle in the course of infection.
    Retrovirology 11/2014; 11(1):93. · 4.77 Impact Factor

Full-text (2 Sources)

Available from
Dec 19, 2014